A gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air enters an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel mixes with the compressed air and burns within the combustion section, thereby creating combustion gases. The combustion gases flow from the combustion section through a hot gas path defined within the turbine section and then exit the turbine section via the exhaust section.
Higher operating temperatures for gas turbine engines are continuously sought in order to increase their efficiency. Though significant advances in high temperature capabilities have been achieved through formulation of iron, nickel and cobalt-base superalloys, alternative materials have been investigated. CMC materials are a notable example because their high temperature capabilities can significantly reduce cooling air requirements. CMC materials generally comprise a ceramic fiber reinforcement material embedded in a ceramic matrix material. The reinforcement material may be discontinuous short fibers dispersed in the matrix material or continuous fibers or fiber bundles oriented within the matrix material, and serves as the load-bearing constituent of the CMC. In turn, the ceramic matrix protects the reinforcement material, maintains the orientation of its fibers, and serves to distribute loads to the reinforcement material.
As certain components are made with a CMC material within the hot gas path of a turbine engine, such as a shroud (e.g., a ring of material surrounding the rotating blades in the turbine section), a thermal mismatch may be introduced between the CMC component and other metal components. That is, the CMC component has a relatively low CTE compared to other metal parts. Thus, the CMC component is much less prone to thermal expansion and contraction during use, compared to metal components of the engine.
As such, a need exists to compensate for the thermal mismatch of the CMC components and the metal components within the gas turbine engine.